Acting Judge Bashier Vally said the error was “fundamental and fatal” and that the decision by the former minister of international relations and cooperation Maite Nkoana-Mashabane must be reviewed and set aside.

Mugabe was accused of using an electrical extension cord to assault Gabriella Engels, a Johannesburg-based model, in August last year.

The then first lady secretly fled the country and Nkoana-Mashabane later granted her immunity.

Lobby group AfriForum and the DA challenged Nkoana-Mashabane’s decision in court.

In his judgment, Vally said the minister was flawed in her understanding of the Promotion of Administrative Justice Act 3 of 2000 in that she “did not merely ‘recognise’ the immunity of Dr Mugabe, she conferred immunity on Dr Mugabe”.

“That the minister has the power to confer immunity on Dr Mugabe is neither doubtful or debatable,” Vally said.

“She, however, has to exercise this power in a manner that is constitutional and lawful.”

Vally said, after considering the contents of the minister’s answering affidavit, there was no doubt that “she came to the conclusion that it was in the national interests of South Africa that Dr Mugabe be clothed with the immunity”.

He further found that Mugabe was not immune to the jurisdiction of the South African courts and the minister’s decision to “recognise” or “confer” immunity upon her was unconstitutional and unlawful.

On that basis, Vally declared Nkoana-Mashabane’s decision to be inconsistent with the Constitution and ordered that it be reviewed and set aside.

AfriForum CEO Kallie Kriel welcomed the court’s decision and called on law enforcement to investigate the matter further and prosecute Mugabe.

“We are elated with this judgment. It means there will be justice for Ms Gabriella Engels, who was the victim in this case,” he said.

“From the start we said the diplomatic immunity that was given to Mrs Mugabe was unlawful. She simply got away because of political reasons.”

Kriel said AfriForum would continue monitoring the case and, if the national prosecuting authority decided not to prosecute, the lobby group’s private prosecuting unit would be ready to prosecute.

DA federal council chairperson James Selfe described the judgment as “a great day for justice [and] the rule of law”.

“This incident is yet another example of how the ANC-led government is happy to abuse its statutory powers at the expense of justice for ordinary South Africans,” he said.

Selfe said an arrest warrant should be issued for Mugabe and called on the South African government to work with all the relevant stakeholders to ensure that Mugabe returns to the country and has her day in court.

“The DA held that Mrs Mugabe was granted immunity simply to shield her from being tried in a court of law,” Selfe said.

“There is nothing in either South African or international law which renders her deserving of diplomatic immunity.”

Department of International Relations and Cooperation spokesperson Ndivhuwo Mabaya said the department was still studying the judgment and would comment later if necessary.

“International Relations and Cooperation Minister Lindiwe Sisulu noted the judgment by the South Gauteng High Court to set aside the 2017 decision by the Department of International Relations and Cooperation to grant former Zimbabwean first lady Grace Mugabe diplomatic immunity.”